Emitter and apparatus equipped therewith

Abstract

To provide an emitter capable of maintaining high reliability even during long-term operation, and a device equipped with the emitter.SOLUTION: An emitter according to the present disclosure includes first and second heaters which generate heat when current is passed through them, an electron source made of a first material which is heated by the first and second heaters and emits electrons, and intermediate members which are interposed between the first and second heaters and the electron source, respectively, and which are made of a second material having a lower thermal conductivity than the first material.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to an electron-emitting emitter and an apparatus equipped with the same. [Background technology]

[0002] Electron emitters are used, for example, in electron microscopes and semiconductor inspection equipment. An emitter comprises an electron source and a heater that heats the electron source to a temperature at which it emits electrons. Patent Document 1 discloses an electron source in which an electron-emitting material (chip) made of a rare earth element hexaboride is sandwiched between a pair of heating elements, and the heating elements are sandwiched between a pair of conductive pillars. In this electron source, an insulating coating is formed on the region of the heating element that is not in contact with the electron-emitting material and the conductive pillars. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2006-12496 [Overview of the project] [Problems that the invention aims to solve]

[0004] Observation of the chip after long-term operation of the electron source disclosed in Patent Document 1 revealed the deposition of hexaboride near the contact point with the conductive support of the heater. It is presumed that the temperature near the contact point with the conductive support of the heater decreases due to heat conduction to the conductive support, so the hexaboride evaporated from the chip cannot re-evaporate and is deposited in this region (see Figure 5(b)). Figure 5(b) is a schematic longitudinal cross-sectional view showing the state in which the material constituting the electron source 11 has been deposited near the heaters 15a and 15b. The deposited material D is attached so as to cover the upper surfaces of the conductive support 17a and 17b and a portion of the upper surfaces of the heaters 15a and 15b that are continuous with them. The arrows in Figures 5(a) and 5(b) represent the current when energized. When the deposited material D is not attached, electricity flows stably through the heaters 15a and 15b as shown in Figure 5(a). In contrast, as shown in Figure 5(b), when the deposited material D adheres, the deposited material D obstructs the stable flow of electricity in the heaters 15a and 15b. In the invention described in Patent Document 1, the decrease in reliability caused by the deposition of hexaboride is suppressed by forming an insulating coating in a predetermined area of ​​the heating element.

[0005] This disclosure provides an emitter and an apparatus equipped therewith that can maintain high reliability even during long-term operation. [Means for solving the problem]

[0006] One aspect of this disclosure provides an emitter. This emitter comprises first and second heaters that generate heat when an electric current is applied, an electron source made of a first material that emits electrons when heated by the first and second heaters, and intermediate members interposed between the first and second heaters and the electron source, respectively, and made of a second material with lower thermal conductivity than the first material.

[0007] In the emitter according to this disclosure, an intermediate member (second material) with a lower thermal conductivity than the electron source (first material) is provided between the electron source and the heater. This configuration makes it possible to operate the heater at a higher temperature compared to when the intermediate member is not provided. This suppresses the deposition of the material constituting the electron source near the heater, thereby suppressing the performance degradation of the emitter caused by this. For this reason, the emitter according to this disclosure can operate stably over a long period of time. The thermal conductivity of the intermediate member is preferably 100 W / m·K or less. The thermal conductivity in this disclosure refers to the value at 20°C measured in accordance with the method described in JIS R1611.

[0008] The emitter according to this disclosure is based on the concept of somewhat inhibiting the efficient heating of the electron source by the heater, while at the same time suppressing the deposition of the material constituting the electron source near the heater (for example, a pair of conductive supports that sandwich the heater) by utilizing the excess heat of the heater. To effectively achieve this, it is preferable that the intermediate member is placed between the electron source and the heater with a certain volume. That is, it is preferable that the length of the shortest path of the intermediate member taken when going from the heater to the electron source is 100 μm or more.

[0009] The electrical resistivity of the intermediate member is preferably sufficiently smaller than that of the heater. The electrical resistivity of the intermediate member is preferably 300 μΩ·m or less. This value of 300 μΩ·m or less suppresses excessive heat generation of the intermediate member due to current flow. The electrical resistivity of the heater is preferably 500 μΩ·m or more. This value of 500 μΩ·m or more allows the heater to generate sufficient heat when current is applied. In this disclosure, electrical resistivity refers to the value at 20°C measured in accordance with the method described in JIS R7222.

[0010] Preferably, the intermediate member covers the surfaces of the electron source other than the electron emission surface. By covering the surfaces of the electron source other than the electron emission surface with the intermediate member, the evaporated material of the electron source during energization can be trapped by the intermediate member. In other words, it is possible to suppress the diffusion of evaporated material from the electron source towards the heater. Therefore, the performance degradation of the emitter caused by deposition of the material constituting the electron source can be suppressed to an even greater extent.

[0011] One aspect of this disclosure provides an apparatus equipped with the above-mentioned emitter. Examples of apparatus equipped with an emitter include electron microscopes, semiconductor manufacturing equipment, inspection equipment, and processing equipment. [Effects of the Invention]

[0012] According to this disclosure, an emitter and an apparatus equipped therewith are provided that can maintain high reliability even during long-term operation. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1(a) is a schematic longitudinal section view showing a first embodiment of the emitter according to this disclosure, and Figure 1(b) is a transverse section view of the emitter shown in Figure 1(a). [Figure 2] Figure 2(a) is a schematic longitudinal cross-sectional view showing a second embodiment of the emitter according to this disclosure, and Figure 2(b) is a transverse cross-sectional view of the emitter shown in Figure 2(a). [Figure 3] Figure 3(a) is a schematic longitudinal cross-sectional view showing a third embodiment of the emitter according to this disclosure, and Figure 3(b) is a top view of the emitter shown in Figure 3(a). [Figure 4] Figure 4 is a thermographic camera image showing the top surface temperature of the emitter according to the embodiment. [Figure 5] Figure 5(a) is a schematic longitudinal cross-sectional view of an emitter relating to a comparative example, and Figure 5(b) is a schematic longitudinal cross-sectional view showing the state in which the material constituting the electron source (lanthanum boride) has been deposited near the heater of the emitter shown in Figure 5(a). [[MODE FOR CARRYING OUT THE INVENTION]]

[0014] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the following description, the same reference numerals are used for the same elements or elements having the same functions, and overlapping descriptions will be omitted. Note that the present invention is not limited to the following embodiments.

[0015] <First Embodiment> Fig. 1(a) is a longitudinal sectional view schematically showing an emitter according to the first embodiment, and Fig. 1(b) is a transverse sectional view of the emitter shown in Fig. 1(a). The emitter 10 shown in these figures includes an electron source 1, a pair of heaters 5a and 5b (a first heater and a second heater) that generate heat when energized, intermediate members 2a and 2b disposed between the electron source 1 and the heaters 5a and 5b, and a pair of conductive support posts 7a and 7b disposed to sandwich these components. The electron source 1 is made of a material (a first material) that emits electrons when heated. The intermediate members 2a and 2b are made of a material (a second material) having a lower thermal conductivity than the material constituting the electron source 1. The heaters 5a and 5b are for heating the electron source 1. The pair of conductive support posts 7a and 7b are for holding the electron source 1 and the like and supplying electricity to the heaters 5a and 5b. Examples of apparatuses including the emitter 10 include electron microscopes, semiconductor manufacturing apparatuses, inspection apparatuses and processing apparatuses. Each configuration of the emitter 10 will be described below.

[0016] (Electron Source) The electron source 1 is made of a first material having electron emission characteristics (electron emission material). A tip portion 1a of the electron source 1 is formed into a conical shape, and electrons are emitted from this tip portion 1a. In the present embodiment, the electron source 1 is exposed on side surfaces 10a and 10b of the emitter 10, respectively.

[0017] In the present embodiment, the shape of the portion other than the tip 1a of the electron source 1 is a square column (see FIGS. 1(a) and 1(b)). The length of the electron source 1 is, for example, 0.1 to 2 mm, and may be 0.2 to 1.5 mm or 0.2 to 1 mm. A length of 0.1 mm or more tends to improve handleability, and a length of 2 mm or less tends to achieve uniform heating. The cross-sectional shape of the square column portion of the electron source 1 is substantially square. The side length is, for example, 0.02 to 1 mm, and may be 0.05 to 0.5 mm or 0.05 to 0.15 mm.

[0018] Examples of electron emission materials include rare earth borides such as lanthanum boride (LaB6) and cerium boride (CeB6); refractory metals such as tungsten, tantalum and hafnium and oxides, carbides and nitrides thereof; and noble metal-rare earth alloys such as iridium cerium.

[0019] From the viewpoints of electron emission characteristics, strength and workability, the electron emission material constituting the electron source 1 is preferably a rare earth boride. When the electron source 1 is made of a rare earth boride, the electron source 1 is preferably a single crystal processed such that the <100> orientation, which facilitates electron emission, coincides with the electron emission direction. The electron source 1 can be formed into a desired shape by electric discharge machining or the like. The side surface of the electron source 1 is preferably a (100) crystal plane, since this is considered to reduce the evaporation rate.

[0020] The material constituting the electron source 1 has a higher thermal conductivity than the material constituting the intermediate members 2a, 2b. The thermal conductivity of the material constituting the electron source 1 is preferably 5 W / m·K or more, and more preferably 10 W / m·K or more. When the thermal conductivity of this material is 5 W / m·K or more, the entire electron source 1 tends to be sufficiently uniformly heated by the heat from the heaters 5a, 5b. The upper limit of the thermal conductivity of this material is, for example, 200 W / m·K. The thermal conductivity of several materials is shown below. • Lanthanum boride (LaB6): 60 W / m·K • Tungsten: 177 W / m·K

[0021] The value of the thermal conductivity T of electron source 1 E The value T represents the thermal conductivity of the intermediate members 2a and 2b. I It is preferable that it be sufficiently larger than the value T of the thermal conductivity of intermediate members 2a and 2b. I The value of the thermal conductivity T of electron source 1 relative to the given value. E The ratio (T E / T I The ratio is, for example, 7 to 13, and may also be 8 to 12 or 10 to 11. Having this ratio within these ranges allows the temperature of heaters 5a and 5b to be moderately high when energized. The temperature of heaters 5a and 5b when energized can be made, for example, 150 to 250°C higher than the temperature of electron source 1. This suppresses the deposition of materials constituting electron source 1 near heaters 5a and 5b.

[0022] (Intermediate member) The intermediate members 2a and 2b are positioned to be in contact with and cover a pair of surfaces 1b and 1c of the electron source 1 (see Figure 1(b)). The intermediate members 2a and 2b are exposed to the sides 10a and 10b of the emitter 10, respectively. It is preferable that the length of the shortest path of the intermediate members taken when traveling from the heater to the electron source is 100 μm or more. That is, in this embodiment, the thickness of the intermediate member 2a (the distance between the electron source 1 and the heater 5a) is preferably 100 μm or more, and may be 100 to 1000 μm or 300 to 800 μm.

[0023] The intermediate members 2a and 2b are made of a material (second material) with a lower thermal conductivity than the material constituting the electron source 1. The thermal conductivity of the material constituting the intermediate members 2a and 2b is, for example, 100 W / m·K or less, preferably 1 to 100 W / m·K, and more preferably 1 to 60 W / m·K. The lower limit of this value may be 2 W / m·K or 3 W / m·K. The upper limit of this value may be 45 W / m·K or 40 W / m·K. A thermal conductivity of 1 W / m·K or more of this material tends to allow sufficient heat from heaters 5a and 5b to be transferred to the electron source 1, while a thermal conductivity of 100 W / m·K or less tends to allow a sufficient temperature difference to be created between heaters 5a and 5b and the electron source 1.

[0024] The materials constituting the intermediate members 2a and 2b preferably contain high-melting-point metals or their carbides, and more preferably contain at least one of metallic tantalum, metallic titanium, metallic zirconium, metallic tungsten, metallic molybdenum, metallic rhenium, tantalum carbide, titanium carbide, and zirconium carbide. Furthermore, this material may also contain at least one of boron carbide and graphite (carbon material), and at least one of niobium, hafnium, and vanadium. Glassy carbon (for example, Glassy Carbon (trade name, manufactured by Reiho Seisakusho Co., Ltd.)) may be used as this material. Boron nitride may also be used as this material. The thermal conductivity of several materials is shown below. • Metallic rhenium: 48 W / m·K Boron carbide: 35 W / m·K Graphite: 80-250 W / m·K • Glassy carbon: 5.8 W / m·K

[0025] A material constituting the intermediate members 2a, 2b has conductivity. From the viewpoint of suppressing excessive heat generation of the intermediate members 2a, 2b caused by energization, the material constituting the intermediate members 2a, 2b preferably has a lower electrical resistivity than a material constituting the heaters 5a, 5b. The electrical resistivity of the material constituting the intermediate members 2a, 2b is preferably 300 μΩ·m or less, more preferably 100 μΩ·m or less. When the electrical resistivity of this material is 300 μΩ·m or less, excessive heat generation of the intermediate members 2a, 2b caused by energization tends to be suppressed. The lower limit of the electrical resistivity of this material is, for example, 0.1 μΩ·m, and may be 0.3 μΩ·m or 1.0 μΩ·m. The electrical resistivity of several materials is shown below. · Rhenium metal: 0.2 μΩ·m · Graphite: 5 to 15 μΩ·m · Glassy carbon: 42 μΩ·m

[0026] (Heater) The heaters 5a, 5b are made of a material having a high electrical resistivity and generate heat when energized. The electrical resistivity of the material constituting the heaters 5a, 5b is preferably 500 to 1000 μΩ·m, more preferably 600 to 900 μΩ·m. When the electrical resistivity of this material is 500 μΩ·m or more, the electron source 1 tends to be sufficiently heated by energization; on the other hand, when the electrical resistivity is 1000 μΩ·m or less, sufficient energization tends to be achieved. Examples of materials constituting the heaters 5a, 5b include pyrolytic graphite and hot-pressed carbon. A typical electrical resistivity of pyrolytic graphite is 800 μΩ·m.

[0027] The electrical resistivity value R of the heaters 5a, 5b H is preferably sufficiently larger than the electrical resistivity value R of the intermediate members 2a, 2b I . The ratio of the electrical resistivity value R of the heaters 5a, 5b to the electrical resistivity value R of the intermediate members 2a, 2b I (R H / R H / R IThis ratio is, for example, 12 to 20, and may also be 13 to 19 or 14 to 18. When this ratio is 12 or higher, the temperature of heaters 5a and 5b can be sufficiently high when energized, and the deposition of materials constituting the electron source 1 near heaters 5a and 5b tends to be suppressed. On the other hand, when this ratio is 20 or lower, the power loss for heating heaters 5a and 5b tends to be reduced.

[0028] <Second Embodiment> Figure 2(a) is a schematic longitudinal cross-sectional view of the emitter according to the second embodiment, and Figure 2(b) is a transverse cross-sectional view of the emitter shown in Figure 2(a). The emitter 20 shown in these figures differs from the emitter 10 according to the first embodiment in that the four sides of the columnar portion of the electron source 1 are covered by the intermediate member 2. That is, in the first embodiment, the intermediate member 2a is interposed between the electron source 1 and the heater 5a, and the intermediate member 2b is interposed between the electron source 1 and the heater 5b, whereas in this embodiment, the intermediate member 2 is interposed between the electron source 1 and the heaters 5a and 5b. By covering the four sides of the columnar portion of the electron source 1 with the intermediate member 2, the diffusion of evaporated material from the electron source can be suppressed, and the heating of the electron source can be made uniform, among other effects. The material of the intermediate member 2 may be the same as the material of the intermediate members 2a and 2b according to the first embodiment.

[0029] <Third Embodiment> Figure 3(a) is a schematic longitudinal cross-sectional view of the emitter according to the third embodiment, and Figure 3(b) is a transverse cross-sectional view of the emitter shown in Figure 3(a). In the emitter 30 shown in these figures, the intermediate member 3 is composed of a columnar portion 3a and a conical portion 3b. An opening 4 is provided at the tip of the conical portion 3b, and an electron source 1 is inserted into the opening 4. The surface at the tip of the electron source 1 is the electron emission surface 1f. The material of the intermediate member 3 may be the same as the material of the intermediate members 2a and 2b according to the first embodiment.

[0030] In this embodiment, the electron source 1 is shaped like a rectangular prism (see Figures 3(a) and 3(b)). The length of the electron source 1 is, for example, 0.1 to 1 mm, and may be 0.2 to 0.6 mm or 0.3 mm. A length of 0.1 mm or more tends to result in good handling, while a length of 1 mm or less tends to reduce the likelihood of cracks. The cross-sectional shape of the electron source 1 is approximately square. The length of its sides is, for example, 20 to 300 μm, and may be 50 to 150 μm or 100 μm.

[0031] In this embodiment, the columnar portion 3a of the intermediate member 3 is rectangular (see Figures 3(a) and 3(b)). The cross-sectional shape of the columnar portion 3a is approximately square. The length of its sides is, for example, 0.5 to 2 mm, and may be 0.6 to 1 mm or 0.7 to 0.9 mm.

[0032] By covering the surfaces of the electron source 1 other than the electron emission surface with the intermediate member 3, electron emission from surfaces other than the electron emission surface is suppressed. The tip of the electron source 1 may or may not protrude from the tip of the conical portion 3b of the intermediate member 3, but it is preferable that it does not protrude. By not having the tip of the electron source 1 protrude from the intermediate member 3, the emission of unwanted electrons, i.e., electron emission to the sides, can be sufficiently suppressed. For example, in order to obtain electrons with a higher current, the tip of the electron source 1 is heated to a high temperature of about 1550°C and a high electric field of several kV is applied to the electron source 1. When such a high electric field is applied, excess electrons may be generated from parts other than the tip of the electron source. These excess electrons may reduce the brightness of the electron beam from the tip or cause unnecessary heating of surrounding electrode components due to the space charge effect. To prevent this, by exposing only the tip surface of the electron source 1 and covering the other surfaces with the intermediate member 3, only a high-brightness electron beam from the tip can be obtained. The tip of the electron source 1 may be recessed relative to the tip of the conical portion 3b of the intermediate member 3.

[0033] By covering the entire side surface of the electron source 1 with the intermediate member 3, the phenomenon known as micro-discharge can be suppressed. In other words, in thermionic emission, electrons are emitted by heating the electron source to a high temperature. As a result, the electron-emitting material evaporates and adheres to the surrounding electrode components, forming fibrous crystals called whiskers. When charge accumulates in these whiskers, micro-discharge is triggered. Micro-discharge destabilizes the electron beam and reduces the performance of the device. By covering the entire side surface of the electron source 1 with the intermediate member 3, the sublimated electron-emitting material is trapped in the intermediate member 3, reducing the amount that adheres to the surrounding electrode components and making micro-discharge less likely. Furthermore, the intermediate member 3 does not have a gap in the circumferential direction, but covers the entire side surface of the electron source 1. Because the intermediate member 3 has no gaps, the emission of electrons to the side can be sufficiently suppressed.

[0034] Although embodiments of the present disclosure have been described in detail above, the present invention is not limited to the above embodiments. For example, in the above embodiments, an electron source having a columnar portion with a substantially square cross-sectional shape was exemplified, but the cross-sectional shape of the columnar portion may be a substantially polygon other than a substantially square, for example, a substantially rectangle, a substantially rhombus, a substantially parallelogram, a substantially triangle (for example, a substantially equilateral triangle), or a substantially regular hexagon. The cross-sectional shape of the opening 4 in the third embodiment does not have to match the cross-sectional shape of the electron source, and may be a substantially circle, a substantially rhombus, a substantially parallelogram, a substantially triangle (for example, a substantially equilateral triangle), or a substantially regular hexagon. [Examples]

[0035] The present disclosure will be described below based on examples and comparative examples. However, the present invention is not limited to the following examples.

[0036] (Examples) An emitter with a configuration similar to that shown in Figure 1 was fabricated using the materials shown in Table 1. The length of the electron source was approximately 0.3 mm, and the length of one side of the columnar section was approximately 100 μm. The thickness of the intermediate member (the distance between the electron source and the heater) was 300 μm.

[0037] [Table 1]

[0038] When the emitter was energized with constant current control so that the electron source temperature reached 1550°C, the heater temperature was 1768°C. Figure 4 is a thermographic camera image showing the top surface temperature of the emitter according to the embodiment. According to the inventors' studies, from the viewpoint of preventing lanthanum boride deposition, it is preferable that the heater temperature be 1700 to 1800°C when the electron source is heated to 1550°C.

[0039] (Comparative example) An emitter with the same configuration as the embodiment was fabricated, except that there was no intermediate component between the electron source and the heater (see Figure 5(a)). When the emitter was energized with constant current control so that the electron source temperature was 1550°C, the heater temperature was 1634°C. [Industrial applicability]

[0040] According to this disclosure, an emitter and an apparatus equipped therewith are provided that can maintain high reliability even during long-term operation. [Explanation of symbols]

[0041] 1... Electron source, 1f... Electron emission surface, 2, 2a, 2b, 3... Intermediate members, 5a, 5b... Heaters, 10, 20, 30... Emitters.

Claims

1. First and second heaters that generate heat when electricity is applied, An electron source comprising a first material that emits electrons when heated by the first and second heaters, Intermediate members are interposed between the first and second heaters and the electron source, respectively, and are made of a second material with lower thermal conductivity than the first material, Equipped with, The shortest path length of the intermediate member through which the electron source passes from the heater is 100 μm or more. The electrical resistivity of the aforementioned intermediate member is 300 μΩ·m or less. The electrical resistivity of the heater is 500 μΩ·m or more. The intermediate member covers the entire side surface of the electron source. An emitter in which the ratio of the electrical resistivity of the heater to the electrical resistivity of the intermediate member is 12 to 20.

2. The emitter according to claim 1, wherein the second material is at least one material selected from carbon, boron carbide, and boron nitride.

3. The emitter according to claim 1 or 2, wherein the second material is glassy carbon.

4. The emitter according to any one of claims 1 to 3, wherein the first material is a material selected from the group consisting of rare earth borides, high melting point metals and their oxides, carbides and nitrides, and precious metal-rare earth alloys.

5. An apparatus comprising an emitter according to any one of claims 1 to 4.

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